The present invention relates generally to a process and mechanism for threading an electrode wire through an aperture in an electrode workpiece in an electrical discharge machining apparatus of the type generally referred to as a travelling wire EDM apparatus. More particularly, the present invention relates to an electrode wire threading method and mechanism wherein the end of the electrode wire is introduced into a jet stream of fluid directed towards the aperture in the workpiece, in order to be guided by the jet stream of fluid through the aperture.
Diverse arrangements have been proposed in the past for automatically threading the electrode wire of a travelling wire EDM apparatus through a hole or aperture pre-drilled in the workpiece. For example, U.S. Pat. No. 3,987,270 and published Japanese application No. 15897/76 disclose such devices. Practical embodiments of the devices disclosed in one or the other of those publications are very difficult to accomplish, if not impossible, because guiding the wire by a stream of liquid is not sufficient to accurately and repeatedly bring the end of the electrode wire directly opposite the aperture in the workpiece.
The present invention overcomes such difficulties and achieves, repetitively, automatic threading of an electrode wire through an aperture in a workpiece.